Intersection

concept in set theory (for the term in geometry, see Q1364910)

collection of sets in which every two sets have the same intersection

theorem on the maximum size of a family of pairwise intersecting sets

220px|thumb|The intersection (red) of two disks (white and red with black boundaries). thumb|right|The circle (black) intersects the line (purple) in two points (red). The disk (yellow) intersects the line in the [[line segment between the two red points.]] 220px|thumb|The intersection of D and E is shown in grayish purple. The intersection of A with any of B, C, D, or E is the empty set.